Some people will take STEP I in lower 6th, then take STEP II and III in upper 6th. They generally do STEP I "just for kicks" or as a warm up for STEP II and III which they will be asked for by Cambridge. I know at least one person who got an S in STEP I this year in his lower 6th and I am in absolutely no doubt will get S,S in STEP II and III next year.